The objective of this proposal is to determine technical feasibility of a fall prevention training system for older adults. Falls are the leading cause of injury and mortality in the elderly. Previous research demonstrated that most older adults can quickly adapt their strategy for responding to a large postural perturbation or tripping incident by changing the biomechanics of their step recovery. The biomechanical step response to a large postural perturbation on a treadmill mimics the biomechanical step response following a tripping or slipping event. This finding offers a unique and novel opportunity to provide a clinical rehabilitation and training tool for this population at high-risk of falling. We will design and fabricate an instrumented, motorized treadmill perturbation platform to provide highly controllable perturbations while walking or at gait initiation. Multi-axis load cells mounted below the platform will provide measurements of ground reaction forces, center of pressure excursions, step length, and response time. In Phase I, we quantify the sensitivity and accuracy of these measurements and the fidelity of perturbation delivered in a laboratory model. In Phase 11, we construct a prototype, instrumented large perturbation treadmill and validate it against an existing laboratory-based system with younger and older adults. A pilot study of 30 older adults will expand the biomechanical research of fall injury mechanisms in response to large postural perturbations. The cost-effective, commercial ActiveStep system developed will be a validated clinical fall prediction and prevention training tool as well as an advanced research tool for further elucidating novel fall prevention strategies.